Touch-sensitive displays are commonly used to provide a touch-based user interface in various devices for many different applications. For instance, touch-based user interfaces are commonly used in medical imaging devices. One or more UI (user interface) objects, such as a measuring caliper, may be used to perform a measurement or other user operation on a medical image. It is typical to use two measurement calipers to measure lengths between various anatomical objects on the medical image. The user would typically use his fingers to manipulate the positions of the measurement calipers in order to select the points defining a distance or length in the medical image. It is also common to use three or more measurement calipers define a circle or ellipse in order to measure an area. Moreover, it is common for measurement calipers to be shaped like a teardrop in order to help the user more accurately select the desired measurement points on the touch-sensitive display. The existing techniques for selecting measurement points with a touch-based user interface all have notable limitations. For example, users may have a difficult time accurately selecting points close to the edge of the display with a teardrop-shaped measurement caliper. Depending upon the orientation of the teardrop-shaped measurement caliper, it may not be possible for the user to position the pointed end of the measurement caliper on the desired anatomy close to the edge of the image. Additionally, it may be very difficult for a user to accurately indicate small distances with existing UI objects for touch-sensitive displays. The user's fingers may commonly obscure some or all of the UI object, making accurate measurements difficult.
Users may experience similar problems with existing UI objects in other applications as well, such as creating free-form drawings on a touch-sensitive display and/or identifying contours in a medical image. For the reasons discussed hereinabove, there is a need for an improved medical imaging device and method for performing a user operation on a medical device with a touch-sensitive display.